The present invention relates to electronic musical instruments in general, and more particularly to improvements in a method and apparatus or system for processing tone signals in electronic pianos, electronic organs or analogous key-operated electronic musical instruments. Still more particularly, the invention relates to a method and system for processing tone signals which are transmitted with a variable delay in an electronic organ or an analogous electronic musical instrument.
A conventional system of the above outlined character is disclosed in German Offenlegungsschrift No. 26 07 136. The tone signal is applied to the input of an analog shift register with periodically varying pulse frequency. To this end, the system employs a voltage-regulated oscillator which is operated with a sinusoidal control potential of 0.6 Hz. This furnishes a phase shift vibrato. By connecting several analog shift registers in parallel in such a way that their pulse frequencies depend from the same control voltages which are out of phase, one can obtain a string or orchestra effect. This effect can be improved if a sinusoidal auxiliary potential of lower amplitude but higher frequency is superimposed upon the control voltage. If the amplitudes of sinusoidal control voltages are different, one can achieve a vibrato effect of highly complex tonality. If the processed tone signal is fed back to the input of the shift register, one can achieve natural frequencies which impart to the tone a celeste vibrato or fading effect.
A drawback of the just described conventional tone processing system is that the interval of delay cannot be reduced at will, i.e., the minimal delay corresponds to that interval which is needed to transport a signal from the input to the output of the analog shift register at a maximum pulse frequency. Moreover, two or more parallel delay paths can be achieved only by resorting to an equal number of discrete shift registers; this contributes to complexity, bulk and cost of the conventional system.